The present invention relates to a gas generator for air bags (hereinafter it is simply referred to as xe2x80x9cgas generatorxe2x80x9d) for use in an air bag system for safely protecting a driver and riders in a vehicle from shock from collisions. Particularly, the present invention relates to a gas generator of cost efficiency having capabilities of maintaining the performance capability of preventing slag in a gas flowing outside.
The gas generators of this type include the one having a housing construction of the so-called single cylinder type and the one having a housing construction of the so-called double cylinder type.
These housing constructions include a welded one and a friction welded one. Either of these two types of gas generators have the following fundamental construction. That is to say, these gas generators have a housing formed by a side cylinder having a plurality of gas exhaust openings; an upper cap closing an upper end of the side cylinder; and a lower cap closing a lower end of the side cylinder.
The housing contains therein an igniter, gas generating agents, and a cooling/filtering member, which are arranged in this order from the center of the housing in a radially outward direction. The cooling/filtering member is formed to enclose the gas generating agents, extending from the upper cap side to the lower cap side.
In the gas generator having this fundamental construction, pressure of the gas generated in the housing rises instantaneously to inflate an air bag at the time of activation of the gas generator, according to the types of gas generating agents or burning conditions. As a result of this, looseness may occur in both end portions of the cooling/filtering member in abutment with the upper cap and the lower cap, then degrading of the hermeticity of the cooling/filtering member at the ends abutting with the upper and lower caps, and as such may cause the slag in the gas to flow outside.
The inventors of this application previously applied for patent in respect of a gas generator having the construction of preventing the slag in gas from flowing outside even when the gas pressure rises instantaneously (Japanese patent application No. Hei 8(1996)-207929)
Specifically, the previously proposed gas generator has, as shown in FIG. 3, a housing 33 composed-of an upper container 31 having a side cylinder 31b having a plurality of gas exhaust openings 38; an upper cap 31a closing an upper end of the side cylinder 31b; and a lower container 32 having a lower cap 32a closing a lower end of the side cylinder 31b. The housing 33 includes therein an igniter 70 having an ignitor element 71 and an inflammation agent 72 sealed by barrier 35, gas generating agents 36, and a cooling/filtering member 37, which are arranged in this order from the center of the housing to a radially outside thereof. The cooling/filtering member 37 is formed to extend from the side of the upper cap 31a to the side of the lower cap 32a. 
Further, the housing 33 has therein metallic foil 39, bypass preventing members 45, 46 and sealing members 40a, 40b. The metallic foil 39 adheres on an inner wall of the side cylinder 31b to cap the gas exhaust openings 38 from the inside. The bypass preventing members 45, 46 are provided at the opposite ends of the cooling/filtering member 37. The bypass preventing members 45, 46 have a L-shaped section, contacting with an inner surface of the cooling/filtering member 37 at the opposite end portions thereof and with inner surfaces of the upper and lower caps 31a, 32a. To ensure the effect of preventing the slag from flowing outside, the sealing members 40a, 40b are provided at end surfaces of the cooling/filtering member 37.
With the gas generator thus constructed, even when the gas pressure in the housing rises instantaneously to inflate the housing, since the bypass preventing members 45, 46 are located at the opposite ends of the cooling/filtering member 37, the slag in the gas can be prevented flowing outside. However, disadvantageously, the gas generator thus constructed has more parts and thus increased costs, due to the provision of the bypass preventing members 45, 46. Particularly in the circumstance in which specs on air bag systems are being standardized, cost reduction is being increasingly requested for gas generators, so cost increase resulting from the increase in component count is a significant drawback.
Accordingly, it is the object of the present invention to provide an improved gas generator at a low cost by improving the construction of inner surfaces of the upper and lower caps 31a, 32a to produce the function that is equal to or better than the function of the bypass preventing members 45, 46 of preventing the slag in the gas from flowing outside through the cooling/filtering member 37, thereby eliminating the need of the bypass preventing members 45, 46 to provide reduction of component count and a resultant improved efficiency in assembling work.
A gas generator for air bags of the present invention comprises a housing formed by a side cylinder with a plurality of gas exhaust openings being closed at its ends by an upper cap and a lower cap; an ignitor, provided in the housing at a center portion thereof, to generate a flame; gas generating agents, provided in the housing at a location radially outside of the to ignitor, to be burnt by the flame to generate gas; a cooling/filtering member provided in the housing at a location radially outside of the gas generating agents to enclose the gas generating agents and extending from the side of the upper cap to the side of the lower cap; and an annular projection for preventing the gas generated by the burning of the gas generating agents from flowing toward an end portion of the cooling/filtering member, the annular projection being integrally formed on at least one of the upper cap and the lower cap so as to abut with an inner peripheral surface of the cooling/filtering member.
This produces the gas generator having, as compared with the gas generator as illustrated in FIG. 3, the feature that the bypass preventing members are replaced by the annular projection integrally formed with the upper cap or the lower cap, thus providing reduced component count as compared to the gas generator of FIG. 3.
The annular projection has the same function of preventing the gas flowing toward the end portion of the cooling/filtering member as the bypass preventing members, and as such can allow a full amount of gas to pass through the entire cooling/filtering member except the end portion thereof. Further, when an instantaneous pressure rise occurs at the time of burning, the annular projection is pressed toward the cooling/filtering member, and as such can produce the operation and effect of a further increased degree of contact between the end surface of the annular projection at the outer diameter side thereof and the end surface of the cooling/filtering member at the inner diameter side thereof. This enables the slag in the gas to be prevented from outside more reliably. This can achieve a gas generator having improved cost efficiency resulting from the reduced component count and the resultant improved assembling workability, while fully maintaining its performance capability of reliably preventing the slag in the gas flowing outside within a permissible range, without using any bypass preventing members shown in FIG. 3 and irrespective of the types of gas generating agents and the burning conditions.
The gas generator for air bags of the present invention may take the embodied form that the side cylinder and the upper cap are integrally formed and the side cylinder and the lower cap are joined to each other by friction welding, to thereby form the housing.
This embodied form provides the following result. When the housing is formed by friction welding, it is difficult to bring the side cylinder and the lower cap into full contact with each other in a uniform condition, and as such may often produce the housing with a gap developing at the opposite ends of the cooling/filtering member. However, even in the gas generator having such a housing, since the projection means prevents the gas flowing toward the end portion, the slag can be, prevented from flowing outside.
Also, the gas generator for air bags of the present invention may take the embodied form that the side cylinder of thin-plate and the upper cap are integrally formed and the side cylinder and the lower cap are joined to each other by welding, to thereby form the housing.
This embodied form provides the following result. The housing having the thin-plate welded structure is easily deformed by the pressure resulting from the gas generated, and as such may often produce the housing with a gap developing between the end of the cooling/filtering member and the cap. However, even in the housing thus structured, since the projection means prevents the gas flowing toward the end portion, the slag can be well prevented flowing outside.
In the gas generator for air bags of the present invention, it is preferable that a space is formed between the cooling/filtering member and the side cylinder.
This provides the following results. The gas is held in the space formed between the cooling/filtering member and the side cylinder prior to being exhausted to the outside passing through the gas exhaust openings, whereby the gas is rendered uniform in pressure in the space. As a result of this, occurrence of the phenomenon of the gas locally passing through the cooling/filtering member toward the gas exhaust openings is prevented, and as such can allow the gas to pass through the entire cooling/filtering member generally uniformly. Thus, although the gas is prevented from directly flowing into the cooling/filtering member at the end thereof by the annular projection, after flowing from a center portion of the cooling/filtering member into the interior thereof, the gas is allowed to easily pass through the cooling/filtering member at the end portion thereof which is located at the back side of the end surface of the projection means at the outer diameter side thereof. This provides an improved efficiency of use of the cooling/filtering member, and as such can achieve size reduction of the cooling/filtering member. As a result of this, size reduction and weight reduction of the gas generator can be realized.
Further, the gas generator for air bags of the present invention may take the embodied form that the housing is provided, around the ignitor, with a center cylinder for joining the upper cap and the lower cap.
With the construction in which the center cylinder for joining the upper cap and the lower cap is provided around the ignitor, the housing is increased in rigidity and thus is made resistant to deformation even when the gas pressure rises at the burning of the gas generating agents. Accordingly, the annular projection can be made relatively small, and resultantly the material costs required for the upper cap and the lower cap can be saved and also the processing time can be shortened, thus providing reduced manufacturing costs.
For the gas generator for air bags of the present invention, it is preferable that the cooling/filtering member has a wall thickness portion to abut with an inner wall surface of the side cylinder.
This provides the result that the pressure of the gas generated presses the cooling/filtering means toward the side cylinder and, as a result, the wall thickness portion is pressed against the side cylinder and is brought into firm contact with it. This enables the slag to be reliably prevented from flowing outside through the gas exhaust openings.
Further, in the gas generator for air bags of the present invention, the gas exhaust openings are hermetically sealed with aluminum foil.
This can provide the result that the combustion pressure can be controlled by, for example, adjusting the thickness of the aluminum foil and also degradation of the gas generating agents resulting from their moisture proof can be prevented.